Sensors for detecting substances are known from the prior art, for example from the field of biosensors, whose function is based on the fact that a substance to be detected is accumulated at a functional surface, that is, is absorbed by this surface, wherein the functional surface forms a selective receptor. Information on the presence, the concentration or the lack of the substance which may be accumulated by the functional surface can then be acquired from the intensity or thickness of an accumulation at the functional surface.